[Studies on the influence of the host system on the result of the neutralization of monodispersed and untreated foot- and mouth disease virus (author's transl)].

Monodispersed foot- and mouth disease virus was obtained by filtration through membranes having a porosity only twice the diameter of the virus. This monodispersed virus was neutralized by immune sera in the same manner as not treated virus. This was shown by the inactivation curve comparing the amount of virus used for the test (calculated as ID50) with the neutralization titre (ND50) or comparing the reduction of infectivity (also calculated as ID50) with the dilution factor of the antiserum. When the virus was assayed by counting the plaque forming units, the monodispersed virus needed more antiserum to be neutralized than a not treated virus suspension. The same mixtures of virus and antiserum were inoculated into different host systems. Using suckling mice there was observed only about 1% of the infectivity measured in primary calf kidney cells. Primary calf kidney cells showed only a tenth of the infectivity seen in BHK-21 cells. The difference between the results in mice and calf kidney cells has been found to be caused by the existence of infectious virus in the mice, which does not cause illness or death in the presence of antibodies. Comparing the same size of cell sheet there is more virus absorbed by BHK-cells in the presence of antibodies than by calf kidney cells. The different results obtained in different hosts for the same virus antibody mixtures are discussed with respect to the detection of small amounts of antibodies and to the limits for the comparison of neutralization titres.